Unviewable HTML

[mgwmgw]

I read email using the Zimbra web client on comcast.next.
I got a couple of messages from the Scrabble application on Facebook.
They contained the following:

This message contains a rich-text HTML portion. Consult your mail client's documentation for information on how to view it.

I have not found any documentation on how to view it.
I tried popping the message up in a separate window.
I tried forwarding it.
This sometimes helps, especially with attachments,
but not this time.

What am I missing?